Electromagnetic sound reproducer system



July 26, 1932. F. A. KOLSTER I ELECTROMAGNETIC SQUND REPRODUCER SYSTEM Filed Aug. 16, 1928 INVENTOR. 1.0K, a, Joaw ATTORNEY Patented July 26, 1.932r

UNITED STATES PATENT Aoli-l'lfce c FREDERICK LA. IKOLS'KILIEIB.,` OF PALO ALTO, CALIFORNIA, ASSIGNOR kZLO FEDERAL TELE- GRAPH COMPANY, OF SAN: FRANCISCO, CALIFORNIA, A. .CORPORATION `CALI- ronnie ELnc'rRoMAGNErIosoUND nnrnonucnn SYSTEM My invention relates broadly to sound reproducers and more particularlytoaSOund reproducer of the electrodynamic type.'

One of the objects -ofmy inventioni isto provide a construction of electrodynamic soundV reproducer `having means form-cilciently reproducing sound overa broad frequency range, f

. Another object ofv my inventionis yto pro- .vide a construction of electrodynamic sound reproducer having means for securing uniform response totone frequencies-pover a wide range of frequencies. for'securing fidelity lin sound reproduction.

15 Still another ob ect of invention'is-lto f `-provide a construction of electrodynamic loud speaker which includes a plurality of voice coils connected in separate circuits responsive to'd-ifl'erent rangesof tone frequencies forsecuring uniform response :over la wide range of frequencies. p

A' further object of myinvention isftoprovide an electrodynamic sound reprod-ucer` having a multiplicity of lvoice coils disposed in the permanent field ofthe electrodynamic p y vthrough theV windings carried `bythe movable system where the -voicecoils are individually connectedin dierent audiofrequency `cirf` cuits responsive `to different ranges of fre-V quencies for securing a uniform 'reproduction of sound overa broad frequency range by the conjoint effect of thevoice coils. Y

A still furtherA object of ymy invention isto providea circuit arrangement 'foran\.eleCtr,o-lv *Y c adjusted as to overlap onead] acentzthe other dynamic .type of loud speaker having4 means '35 for efiicicntly operating from the'relatively I heavy current `existent in theoutputsystem f Y n f Y vide means for independentlyy tuningithe different branches tothesele'ctedrange of fre-l of a power amplifier.

My invention will stood from thespecification hereinafter following by reference to *the-following,specifi-V through the electrodynamic sound' reproduce er of my invention; Fig. ,2`isijan enlarged l "windings connected .inA the separate branch l in Letters Patent 1,637,119 vto Frederick A.

be more clearly undencross-sectional view ofthe electrodynamic operating mechanism in the sound kreproducerof my invention illustratingthe multiple circuits in theoutput system of the power amplifier; and Fig. 3 is achart illustrating i the principle kkof my invention.

n In the development .of the electrodynamic type of sound reproducer ofthe class shown Kolster andxSigurd A.1Sollie, I have 'found y v that the efficiency of the soundreproducer maybe substantially `increased kby the provision of afmultiple winding on fthe movable element ofV the electrodynamic sound V,reproducer- By providing independent paths from theoutput systemthrough-each of the f windings on the movableieleln@Tnt I am able y to secure uniform response over a relatively widerange of frequencies for improving lthe" reproduction of sound. Y

,My invent-ion nds particular application in electric phonograph systems fand in radio receiving apparatus `rwhere a power amplifier 1s employed yto `supply variable currents'vo element of ythe electrod-ynam fsystem. [I

- have found that by dividing the path of the current through the moving coil into 'a `plu-a and; thereby rendery the reproduction of soun 80 uniform overga -widelfrequency range..v lprolwhich housesthe electrodynamic; operating y mechanism which includes the rcentral pole "9 member 2 on which is disposed the electromagnetic winding 8. A plate member 4 is secured to the front of the casing 1 and is provided with a central annular aperture 5 through which the pole member 2 projects. The conical shaped sound reproducing diaphragm is supported by means of a flexible annular web member 6 which is secured to the surface of the conical shaped sound reproducing diaphragm 7 in a position intermediate the apex 8 and peripheral edge 9. The peripheral edge 9 is connected to a flexible web 2S which is supported in an annular `frame structure composed of channel shaped members 24-25 riveted one to the other. The channel shaped members are supported in predetermined relation tothe lelectrodynamic system by means of arms 26. The

web 6 is suitably secured to the ring structure 10 which is carried by the plate 4. A tubular member 11 of insulating material is connected by means of metallic member 12-with the conical shaped sound reproducing diaphragm 7. The tubular member 11 carries a multiplicity of independent windings. For the purpose of illustrating the principle of my invention I have shown two 'such windings disposed one upon the other,

the winding in one layer being designated as voice coil 14, and the winding in the other layer being designated as voice coil 15. The

f windings all operate within a common mag- Yiietic field provided by the electiomagnetic winding 3 vand the lines of force which pass throughv the annular gap formed in aperture 5 between front plate 4 and pole member 2. rIhe pole member 2 is cut away at the front Y thereof, as indicated at 16, to receive the apex V8 of the conical shaped sound reproducing diaphragm 7 in a position free for vibratory motion.

Independent paths Vare provided through the voice coils from the output system of the power amplifier. In Figure 1 I have designated electron tube 17 as constituting the last stage of power amplification in an electric phonograph system or in a radio receiving apparatus. The output circuit of the power amplifier system includes an output transformer designated at 18 having a secondary winding 19 which connects to the common point 2() of the ends of the voice coils 14 and 15. The opposite ends of the Vvoice coils 14 and 15 connect through diEerent branch circuits with tlie opposite side of the secondary winding 19. I have illustrated condenser 21 in series with voice coil 15.

in series with voice coil 14 and condenser 22 These condensers have that capacity necessary to tune the branches to particular ranges of audiofrequencies according to the characteristic curves illustrated in Fig. 3. The frequency response curve of voice'coil 14 drops off at a point where the frequency response curve of voice coil 15 rises by virtue of the differently tuned branch circuits, giving as a result the combined effect of voice coils 14 and 15 or a response curve which is substantially uniform over a wide range of frequencies. While I have illustrated two voice coils in two separate branch circuits, it will be understood that a multiplicity of voice coils may be provided for securing efficient reproduction over a broad frequency range.

Thile I have described my invention in a certain preferred embodiment, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim asnew and desire to secure by Letters Patent of the United States is as follows:

1. In a sound reproducer of the electrodynamic type a sound reproducing diaphragm, an electromagnetic field system having a magnetic gap therein, a coil support carried by said diaphragm and projecting into said gap and a plurality of independent windings each in series with a condenser and carried by said coil support and operative by the conjoint influence of currents in said plurality of windings for imparting vibrations to said sound reproducing diaphragm.

2. A sound reproducer of the electrodynamic type comprising a field magnet system including an annular magnetic gap, a sound reproducing diaphragm, independent ciicuits each having a condenser in series therewith responsive to different ranges of audio"l 4. In a loud speaker, the combination of* a field magnet having an annular air gap, and a cone diaphragm carrying a speech coil adapted to vibrate axially in said air gap, said coil consisting of at least two windings each having a condenser in series therewith and so connected in circuit as to respond most efiiciently to the higher and lower tonal register, respectively.

5. A. sound reproducer of the electrodyiiamic type, comprising a sound reproducing diaphragm, a multiplicity of separate windings supported by said diaphragm, an electromagnetic field common to all of said windings, said windings eacli having independent series connections to separately tuned branch 

